Reinforced beam section and a method of producing it

ABSTRACT

The invention relates to reinforced beam sections produced by forming the cross-sectional configuration of wood particle board, e.g. such as have been provided with bonded-in reinforcing threads (4,5,6,32,48). The latter have thereby been laid in the zones (33,34,45) of the boards where the beam section configuration changes direction during the formation of the beam. Beam sections in accordance with the invention will be light, corrosion-resistant and saving on material as well as having high breaking strength, due to the reinforcement. The field of use for such beam sections is very varied, but among more obvious uses may be mentioned those as beams in housing structures and different kinds of batten in the building trade. A method of laying the reinforcing threads in predetermined zones in the boards is also embraced by the invention.

The present invention relates to a reinforced beam section and a methodof producing it by means of compression moulding wood particle boardswhich are internally reinforced with glass fibre at least in zones.

The beam sections primarily envisaged for the application of the presentinvention are light building beam structures, e.g. with L, U, Z or Vsection. In the prior art, such beam sections are usually made frommetal sheeting which is folded or stamped to the desired sectionconfiguration. Rolled or extruded aluminium sections are also available.Although such metal beam structures have satisfactory strengthproperties, they have certain disadvantages, e.g. sensitivity tocorrosion and high thermal conductivity which may lead to so-called"cold bridges" when used, especially in respect of outer walls.

The increased use of light beam sections of metal within the buildingtrade has been primarily brought about by the heavily increasing pricesof solid, first-class timber which has up to now been the dominatingmaterial in wall beams, floor joists, battons etc. in house structures,for example. To avoid the avoid above-mentioned disadvantages with metalbeam structures while holding weight and cost levels down, there havebeen trials made to produce simplified light beam structures in wood. Asexamples of such structures can be mentioned I-beams with a webfabricated from wood fibre board and fastened between two timber studs.There are also structures where two thin wood fibre board sheets havebeen proviede with an intermediate filling of foamed plastics or otherinsulation material and fixed along their edges against intermediatespacer battons. The machining and assembling operations required in theproduction of these composite timer beams reduce to a certain extent thematerial savings gain, thus increasing the cost which is to be comparedwith the cost of using solid joists or the like.

A basic concept in the realization of the present invention has beenthat compression moulding of light sheet metal structures in anappealing method of production in itself. If the sheet metal materialcould be replaced by wood particle material, much would be gained fromthe aspects of machining and use. In other words, a compression-mouldedbeam of wooden material should be cheap to manufacture, light andcorrosion-resistant and thus be well-suited for use in structures wherelight building beams, joists and the like are used.

Compression moulding is already known per se in woodworking.Accordingly, such items as seat bottoms and trays are produced bycompression moulding (providing the item with a particular configurationunder pressure and heat) of plywood, laminated wood etc. Wood particuleboards can in a similar way be processed by compression moulding. Theproblem in using this technique in the manufacture of beams from woodpartiicle boards would lie primarily in obtaining required materialstrength in the finished beam. As opposed to board material andlaminated products produced by compression moulding, beam sectionstructures are subjected to very high concentrated loads and shearingloadings which are intended to be taken up and transmitted by means of asection configuration suited to each individual purpose. The basic ideahereby is that the different beam elements shall be put together so thatthe loading forces acting thereon will act substantially in thelongitudinal direction of the beam member towards a point of flexurewherein the section merges at substantially a right angle into anotherbeam member. As a result of the above-mentioned conditions, materialstresses will be greatest in the angled zones of the beam section. Thesestresses will be of such a magnitude that a conventionally compressionmoulded beam of wood particle board would not resist the loadingsprevailing, and would buckle for relatively modest bending and shearingloads, beginning in the angled zones of the section.

The production of a compression moulded beam section fabricated fromwood particle board has now been enabled by means of the presentinvention. In accordance with the invention this has been enabled by theparticle board being provided already during manufacture with embeddedreinforcing strands of glass fibre which have been positioned in thezones of the borad where it has been formed by the compression mouldingto form the beam secton.

The invention will now be described, while referring to the appendeddrawings, whereon:

FIG. 1 illustrates a channel section in accordance with the invention,

FIG. 2 illustrates a batten used in conjunction with roofing,

FIG. 3 illustrates a filament- or thread-reinforced wood particle boardfor manufacuring the batten in question, and

FIG. 4 schematically illustrates a section of the production line wherethe invention is applied in the manufacture of wood particle boards.

In the channel illustrated in FIG. 1, reinforcing threads 4, 5, 6 havebeen laid in the zones between web 1 and flanges 2, 3. In this case thereinforcing threads are of glass fibre, one thread 4 being laid zigzagand two threads 5, 6 being laid straight in the direction of travel ofthe fibre mass during manufacture, the zigzag thread being suitably laidso that it surrounds the other two threads to form a rope ladder-likereinforcement. How the reinforcing threads are laid in the board isexplained in conjunction with the description in connection with FIG. 4.

A batten in accordance with the invention is illustrated in FIG. 2 theprofile of the batten being substantially similar to that of known metalsheet structures for the same purpose. In this case the loads aregreatest at the angle between sides 23, 24 projecting away from the weband free flanges 21, 22 of the profile. Reinforcement 25 has thereforebeen arranged in the zones at the junctures of portions 21, 23 and 22,24. In this case it has also been found suitable to reinforce theflanges themselves, these being used to attach the batten to asubstructure by means of nailing or riveting. Consequently, thereinforcing zone has been arranged to cover the greater part of theflanges.

Flat wood particle boards in which reinforcing threads of glass fibrehave been provided in given zones during the manufacturing process ofsaid boards are used, as previously mentioned, as the semi-finishedproduct in manufacturing beam sections in accordance with the invention.Such a board for the manufacture of battens according to FIG. 2 is shownin FIG. 3. In this board 31 reinforcing threads 32 have been laid inzones 33, 34 within which the angle bend between the flange and the sideoutstanding from the web will be made during moulding the finishedsection. The boards are suitably manufactured with a width such that aplurality of batten blanks are obtained after longitudinal parting 35 ofthe boards.

FIG. 4 schematically illustrates a suitable method of providing theinventive reinforcement during manufacture of the boards, as well as theequipment required. As one of the first operations in a continuous boardmanufacturing process, a wood particle mass for providing a bottom layer41 of the board is supplied from a wood praticle stock vessel 42. Thelayer is advanced in the direction of the arrow 43 and reinforcingthreads 44 are laid out on top of the bottom layer so that thereinforcement will cover a predetermined zone 45 on the board-to-be. Inthe next phase of this principally sketched continuous manufacturingprocess, a top wood particule layer 46 of the board is applied from astock vessel 47. A suitable method of continuously forming a network 48of reinforcing threads has been illustrated in the Figure by twostationary spools or bobbins 49,50 and a bobbin 51 arranged to circleround the bobbins 49,50. The preparation of the threads with an adhesivebefore laying on the bottom layer has been schematically illustrated bya vessel 52 containing the adhesive. Manufacturing equipment of the kindshown, when applied in an embodiment suitable for production, must ofcourse be provided with a pluality of details and means, not shown here,for driving, advancing, guiding and controlling the different steps inthe manufacturing operation. It is also assumed that in practicalproduction it will be advantageous to arrange serveral parallel unitsfor providing zonal reinforcement across the width of the board in eachboard manufacturing line. The other equipment required for boardmanufacture, such as dewatering, drying and hardening has not been shownin the Figure either.

A suitable type of reinforcing thread has been found to be a glass fibrethread of the so-called "rooving-type", the thread being formed by abundle or cluster or glass fibre filaments with about 2000-4000 glassfibre fibrills with a thickness of 0.010-0.040 mm.

A suitable adhesive for use in preparing the reinforcing threads beforethey are laid in the wood particle mass is a polymer adhesive, e.g.water-emulsified polyvinyl acetate (PVA) glue with a water content of40-60%. The application of a suitable adhesive to the threads has beenfound to be extremely important for obtaining a satisfactory bondbetween the reinforcing threads and the wood particle composition, aswell as between the individual glass fibre filaments incorporated in thethreads. With regard to the board production process, a water-based glueshould be used, its viscosity being adjusted such that rapidimpregnation of the thread, i.e. proper coating of the individualfilaments, is obtained. However, the viscosity should not be so low asto risk too great seepage into the wood particle composition, and forthis purpose a water content of the adhesive emulsion of about 40-60%has been found suitable.

I claim:
 1. A reinforced beam section provided by forming, e.g.compression molding, a board-shaped semi-finished product, characterizedin that said product is a wood pulp board known per se havingreinforcing threads preferably of glass fiber embedded and bondedtherein at least in predetermined zones, said zones are zones aroundareas of inflection, i.e. changes in direction in the configuration ofthe finished section and said reinforcing threads are in the form ofcontinuously running threads, crossing over from one side to another ofsaid inflection points in the configuration of the section in aplurality of places in the longitudinal direction of said inflectionpoints.
 2. A section as claimed in claim 1, characterized in that thereinforcing threads are glass fiber threads comprising bunches orclusters of glass fiber filaments having 2000-4000 filaments with athickness of 0.010-0.040 mm.
 3. A section as claimed in claim 1 or 2,characterized in that the threads are bonded in the material of theboard with the aid of an adhesive comprising a water-based polymer glue.4. A section as claimed in claim 3, characterized in that the adhesiveis a polyvinyl acetate glue, adapted with a water content of 40-60% toimpregnate the reinforcing threads, i.e. to coat the filaments of whichthe threads comprise.
 5. A method of producing a reinforced beam sectionas claimed in claim 1, characterized in that the section is formed, e.g.by compression molding of wood pulp board known per se, which isprovided in conjunction with its manufacture with embedded reinforcingthreads, preferably from glass fiber, said threads being laid inpredetermined zones in said boards and in continuously running threadscrossing over from one side to another of said inflection points in theconfiguration of the section in a plurality of places in thelongitudinal direction of said inflection points after the compressionmoulding and in said zones the inflection points of the beam sectionthereafter are provided during the process of forming the section.